The present invention relates generally to wireless communications systems, and more specifically to spectrum management techniques for wireless broadband communications systems that provide for increased data throughput and link availability through more efficient use of the electromagnetic spectrum allocated to the system.
In recent years, there has been an increasing need for wireless communications systems capable of carrying broadband data. Such a need has arisen for a variety of reasons, including the difficulties that users often experience in obtaining high speed Internet access service in some remote areas, and the convenience that wireless systems generally afford to users wishing to set up communications links and networks accessible from locations within urban environments or from locations dispersed across significant geographical distances. A conventional wireless broadband communications system can be configured as a line-of-sight (LOS) system or a non-line-of-sight (NLOS) system. The conventional LOS system typically includes a directional antenna deployed at one or more user locations within the line-of-sight of an antenna at a base station. The conventional NLOS system is typically configured as a multiple input multiple output (MIMO) system including a first plurality of antennas deployed at one end of a communications link, and a second plurality of antennas deployed at the other end of the communications link. Both the LOS system and the NLOS system may be employed in point-to-point and point-to-multipoint applications, in which a transmitter transmits signals over multiple communications channels using known space-time coding and modulation techniques, and one or more receivers capture the transmitted signals and employ signal processing techniques to decode and demodulate the signals to recover user data.
One problem facing conventional wireless broadband communications systems, whether they are configured as LOS or NLOS systems, is that the bandwidth capacity of the communications channels available to the systems is often limited, resulting in severe constraints in the communications capacity of the overall system. In a wireless communications system, such channels are typically defined within a limited portion of the electromagnetic spectrum allocated to the system. To achieve more efficient use of the allocated spectrum, wireless communications systems have employed digital communications techniques that allow data packets corresponding to separate communications sessions to be transmitted along multiple shared channels, obviating the need for a single dedicated channel for each communications session. Such techniques are frequently employed in wireless communications networks including one or more wireless LANs (WLANs), which utilize data packet protocols to communicate between the various nodes of the WLAN. The operational parameters for such WLANs are described in the IEEE 802.11 standard.
More recently, the use of shared frequency bands has exacerbated the problems relating to the constraints in the communications capacity of wireless broadband communications systems. Such a shared frequency band for WLANs is the unlicensed frequency band located at 5 GHz. Due to the unlicensed nature of the shared 5 GHz band, more than one WLAN operating in the 5 GHz band may be deployed within the same geographical area. Further, other types of wireless communications systems and radar operating in the 5 GHz band, or generating frequency harmonics having components in the 5 GHz band, may also be deployed within the same geographical area. As a result, the levels of noise and interference on the channels available to wireless communications systems are likely to increase, thereby significantly reducing data throughput and link availability.
It would therefore be desirable to have a wireless broadband communications system that makes more efficient use of the electromagnetic spectrum allocated to the system, and that avoids the drawbacks of the above-described conventional wireless communications systems.